Dissorophus

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Dissorophus
Temporal range: Kungurian, 280–273  Ma
Dissorophus multicinctus.JPG
Dissorophus multicinctus skeleton
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Order:† Temnospondyli
Family:† Dissorophidae
Subfamily:† Dissorophinae
Genus:† Dissorophus
Cope, 1895
Type species
†Dissorophus multicinctus
Cope, 1895

Dissorophus (DI-soh-ROH-fus) (meaning "double roof" for two layers of armor) is an extinct genus of temnospondyl amphibian that lived during the Early Permian Period about 273 million years ago. Its fossils have been found in Texas [1] and in Oklahoma [2] in North America. Its heavy armor and robust build indicate Dissorophus was active on land, similar to other members of the clade Dissorophidae that are known from the Late Carboniferous to the Early Permian periods. Dissorphus is distinguished by its small body size, disproportionately large head and short trunk.

Contents

The American paleontologist Edward Drinker Cope first briefly described Dissorophus in 1895, [3] likely deriving the genus name from Ancient Greek δισσός/dissos "double" and ὀροφή/orophe "roof" to refer to the double layer of armor formed by horizontal "spinous branches" at the top of the neural spines of the vertebrae that "touch each other, forming a carapace" with overlying rows of bony osteoderms that form an armored "dermal layer of transverse bands which correspond to the skeletal carapace beneath," a feature expressed as well in the type species name multicinctus, meaning "many-banded" in Latin. Cope referred to the animal as "a veritable batrachian [amphibian] armadillo."

DeMar mentions Boulenger's interpretation of Dissorophus as “remarkable for an extraordinary exo- and endo-skeletal carapace", [4] reflected in the name Dissorphus multicinctus for its double layered armor. [5]

History

Additional specimens of Dissorophus were later collected by the Museum of Comparative Zoology at Harvard College and the University of Chicago, described by the paleontologists Williston, Case and Romer. Williston (1914) divided the Dissorophidae into two subfamilies: Aspodosaurinae and Dissorophinae. He distinguished the Aspodosaurinae as having an open otic notch and single layered armor (one armor segment per vertebral segment), and Dissorophinae as having a closed otic notch and double layered armor (two armor segments per vertebral segment). [4]

Classification

Below is a cladogram from Schoch (2010). Schoch developed his cladogram based on an analysis of anatomical features of dissorophids. He found that Dissorophus, Broiliellus texensis, Broiliellus brevis and Broiliellus olson all share a pointed snout as a common feature. [6]

Dissorophoidea

Description and Paleobiology

Skull

Dissorophus multicinctus skull in anterior view showing frontal depressions 3 Dissorophus multicinctus 2.JPG
Dissorophus multicinctus skull in anterior view showing frontal depressions

Schoch and Sues describe the skull of Dissorophus multicinctus as “short and broad posteriorly”. DeMar and Williston mention that the skull has two equal sides and it is flat posterior to the orbit, but curved and has depressions from anterior to margins. In addition, the skull surface shows deep circular pits or depressions situated on posterior portions of the frontals and bound by narrow ridges between them and thus difficult to distinguish sutures. [1] [7] [8]

According to DeMar, the skull depth increases posteriorly and decreases anteriorly when in lateral view. He points out another prominent feature of Dissorophus which is an enlarged otic notch. Measuring up to 3.5 cm in length, the otic notch of Dissorophus is relatively deeper than some members of the family Dissorophidae who possess shallow otic notches. The presence of an otic notch firmly assures that dissorophides are indeed unified with the amphibian family because this feature present in all amphibians and lost in later amniotes. DeMar also adds that the depth of the otic notch relates to the length of the skull. In this case, short skulls would have shallow otic notches and longer skulls would possess deeper otic notches. [1]

Carroll (1964) makes a similar observation as DeMar in Broiliellus brevus that has a short skull and therefore a shallow otic notch, as expected. On the other hand, Bolt makes a crucial comment, that the specimens used to describe these anatomical features by both DeMar and Carroll are based on that assumption that they are in "adult configurations". [9] [10] DeMar mentions that the external nares is enlarged and measures up to 1 cm long in larger specimens. [1]

On this note, Williston adds that the external naris are elongated along the skull margins, resulting to an oval shaped outline and oriented laterally and anteriorly. [1] [7]

The orbits of Dissorophus are relatively large, circular, and oriented dorsally than laterally. As DeMar describes, the orbits are large enough to intersect with the frontals, palatines, post orbitals, lacrimals, and jugals. [1]

DeMar also makes points out a crucial feature that suggest why Dissorophus and Broileillus are closely related to one another than any other species. This feature at the region where maxillary, quadratojugal and jugal meet. In this case, he illustrates that the jugal overlaps the quadratojugal and maxillary, thus extending to the tooth rows. This feature was also observed by Carroll (1964) on Broiliellus brevis, Conjuctio and Dissorophus angustus. Thus, this feature gives another explanation to the relationship between Dissorophus and Conjunctio, keeping in mind that Dissorophus and Broiliellus are more closely related to each other because they both have a pointed snout while Conjunctio does not. [1] [10]

Ventral view of a Temnospondyl Skull showing Interpterigoid Vicuity Interoterygoid vicuity.gif
Ventral view of a Temnospondyl Skull showing Interpterigoid Vicuity

Another distinct feature that Dissorophus has is that the maxillary teeth extend further back ventral to the squamosal. DeMar explains this extension of teeth further back correlates with the jugal overlap on the maxillary and quadratojugal. In addition, DeMar clarifies that the contact between vomer and pterygoid is lost resulting to palatine contributing to an enlarged interpterygoid. [1]

Lower Jaw

Dissorophus multicinctus skull in Lateral view including dentary 3 Dissorophus multicinctus.JPG
Dissorophus multicinctus skull in Lateral view including dentary

Williston's anatomical analysis on Dissorophus reveal that there are about thirty five teeth on the dentary. [7] Additionally, DeMar's mentions that the entire lower jaw is covered by dermal pitting except for the region of coronoid process. He also mentions that the coronoid process extends anteriorly and serves as an attachment point for muscles and thus the most probable diet inferred would be a carnivore likely to prey on smaller animals such as insects and smaller animals. DeMar also comments on a distinctive feature that is only present in Dissorophus multicinctus and not any other dissorophids. He explains the presence of a ventral flange that interrupts the continuity of the lower jaw. Connecting to the ventral flange is a pitted surface of angular that “continues on the ventral edge and projects medially forming a small shelf.” He concludes that this arrangement of lower jaw is not found in any other dissopophid, however, the angular projection ventral to the ventral flange is also developed in Briolielus. [1]

Limbs

Williston explains that the humerus and femur of Dissorophus are solidly built and stouter. The humerus has "deep lateral curvatures and wide supracondicular ridges" while the femur is a lot stronger built compared to the humerus. He also mentions that the articular surface of Dissorophus femur is "flattened with sharp rims on the antero-posterior convexity". He adds that both femur and humerus are both "expanded on the inner and outer side and narrow in the middle". [7]

Carapace and Vertebrae

The carapace is another distinctive feature present in Dissorophus. Williston describes this feature as a heavy bony covering that is not necessarily broad, but long and heavy. The dorsal section is deeply pitted and the ventral section is rather smooth. [7] In addition, Dilkes's findings show that the osteoderm is composed of an internal section and external section that are “expanded laterally”. His distinction between an internal and external section is such that the internal section is associated with a flange. The flanges are deeply notched and the edges of these notches serve as attachment points to the neural spine, this explains his hardships in trying to decipher regions of the neural spine. On the other hand, the external series are positioned anterior to the internal series. He also adds that both series are likely fused together by interosteodermal ligaments. This osteoderm feature that Dilkes makes directly correlates to Bolt's interpretations that Dissorophus has a double layered osteoderm comprising both the internal series and external series. [7] [5]

In terms of locomotion, Dilkes mentions that compared to Cacops, Dissorphus likely had a more flexible vertebral column in terms of lateral flexion and axial rotation. Limitation to locomotion is solely based on anatomy of the osteoderms. As Dilkes explains, coupling between lateral flexion and axial rotation throughout the vertebrae, translates to limited locomotion. In the case of Cacops, Dilkes's interpretation on the 20-degree angle of inclination of the zygapophyses indicate that coupling between lateral flexion and axial rotation is highly limited. In addition, there is extensive overlap between internal series and external series which contributes to a limitation of lateral flexion. In the case of Dissorophus, Dilkes gives more detail that there is larger angle of inclinations of zygapophyses indicating that there is greater coupling between the axial rotation and lateral flexion despite insertion of the flanges in the neural spine.

In conclusion, both DeMar and Dilkes clarify that the osteoderm growth covers the first sections of the anterior vertebral column and grows posteriorly with fusion of the next posterior vertebral sections. This means that reduction of flexibility starts anteriorly and proceeds posteriorly, thus it is likely that "as juveniles both Cacops and Dissorophus had greater vertebral flexibility" as mentioned by Dilkes. [11] [1]

Paleoenvironment

Life restoration DissorophusDB22.jpg
Life restoration

Modern amphibians are semi-aquatic. According to DeMar, Dissorophus multicinctus had made a full transition on terrestrial land, indicated by the presence of a dermal armor that made it less dependent on water and better adapted to active life on land. [1]

His hypotheses on terrestriality include:

Some functions of the dorsal armor suggested by DeMar include;

DeMar's suggestions on terrestriality and functions of dermal armor directly correlates to the Geological location at which Dissorphus multicinctus fossils are found. [1] According to both Williston, Schoch and information from the Paleobiology database , Dissorophus fossils are found in the Clear Fork Division of the Texas Red-beds of Arroyo formation. [6] [1] [7]

Related Research Articles

<i>Cacops</i> Extinct genus of amphibians

Cacops, is a genus of dissorophid temnospondyls from the Kungurian stage of the early Permian of the United States. Cacops is one of the few olsoniforms whose ontogeny is known. Cacops fossils were almost exclusively known from the Cacops Bone Bed of the Lower Permian Arroyo Formation of Texas for much of the 20th century. New material collected from the Dolese Brothers Quarry, near Richards Spur, Oklahoma in the past few decades has been recovered, painting a clearer picture of what the animal looked and acted like.

<span class="mw-page-title-main">Dissorophidae</span> Extinct family of temnospondyls

Dissorophidae is an extinct family of medium-sized temnospondyls that flourished during the late Carboniferous and early Permian periods. The clade is known almost exclusively from North America.

<i>Platyhystrix</i> Genus of amphibians (fossil)

Platyhystrix is an extinct temnospondyl amphibian with a distinctive sail along its back, similar to the unrelated synapsids, Dimetrodon and Edaphosaurus. It lived during the boundary between the latest Carboniferous and earliest Permian periods throughout what is now known as the Four Corners, Texas, and Kansas about 300 million years ago.

<i>Acheloma</i> Extinct genus of amphibians

Acheloma is an extinct genus of temnospondyl that lived during the Early Permian. The type species is A. cumminsi.

<i>Laidleria</i> Extinct genus of amphibians

Laidleria is an extinct genus of temnospondyl that likely lived between the Early to Middle Triassic, though its exact stratigraphic range is less certain. Laidleria has been found in the Karoo Basin in South Africa, in Cynognathus Zone A or B. The genus is represented by only one species, L. gracilis, though the family Laidleriidae does include other genera, such as Uruyiella, sister taxon to Laidleria, which was discovered and classified in 2007. 

<span class="mw-page-title-main">Trematopidae</span> Extinct family of temnospondyls

Trematopidae is a family of dissorophoid temnospondyls spanning the late Carboniferous to the early Permian. Together with Dissorophidae, the family forms Olsoniformes, a clade comprising the medium-large terrestrial dissorophoids. Trematopids are known from numerous localities in North America, primarily in New Mexico, Oklahoma, and Texas, and from the Bromacker quarry in Germany.

<i>Aspidosaurus</i> Extinct genus of amphibians

Aspidosaurus is an extinct genus of dissorophoid temnospondyl within the family Dissorophidae.

<i>Anconastes</i> Extinct genus of amphibians

Anconastes is an extinct genus of dissorophoid temnospondyl within the family Trematopidae. It is known from two specimens from the Late Carboniferous Cutler Formation of north-central New Mexico in the southwestern United States. The genus name derives from two Greek roots, ankos and nastes ("inhabitant"), which refers to the type locality of El Cobre Canyon where the specimens were found. The specific name is derived from the Latin word vesperus ("western"). The more complete specimen, the holotype, is a partial skull with articulated mandibles and a substantial amount of the postcranial skeleton. The less complete specimen, the paratype, consists only of the right margin of the skull with an articulated mandible.

<i>Broiliellus</i> Extinct genus of amphibians

Broiliellus is an extinct genus of dissorophoid temnospondyl within the family Dissorophidae. Broiliellus is most closely related to the genus Dissorophus, and both have been placed in the subfamily Dissorophinae. Broiliellus is known from five species from the Early Permian: the type species is Broiliellus texensis, and the other species are Broiliellus brevis,Broiliellus olsoni, Broiliellus arroyoensis, and Broiliellus reiszi. An additional species, Broiliellus novomexicanus, which was originally named Aspidosaurus novomexicanus, is now thought to fall outside the genus as a member of the subfamily Eucacopinae.

<i>Conjunctio</i> Extinct genus of amphibians

Conjunctio is an extinct genus of dissorophid temnospondyl amphibian from the early Permian of New Mexico. The type species, Conjunctio multidens, was named by paleontologist Robert L. Carroll in 1964.

<i>Ecolsonia</i> Extinct genus of amphibians

Ecolsonia is an extinct genus of trematopid temnospondyl. Its phylogenetic position within Olsoniformes has been historically debated, but it is presently considered to be a trematopid.

Iratusaurus is an extinct genus of dissorophoid temnospondyl within the family Dissorophidae. It was described by Gubin (1980) on the basis of a fragmentary posterior skull. It is estimated to have been comparably large to Kamacops, another Russian dissorophid, but little more can be said about it, and it is rarely mentioned in comparative descriptions and has never been tested in a phylogenetic analysis. Distinguishing features include a large, triangular otic notch and a median crest on the postparietals.

<i>Heleosaurus</i> Extinct genus of tetrapods

Heleosaurus scholtzi is an extinct species of basal synapsids, known as pelycosaurs, in the family of Varanopidae during the middle Permian. At first H. scholtzi was mistakenly classified as a diapsid. Members of this family were carnivorous and had dermal armor, and somewhat resembled monitor lizards. This family was the most geologically long lived, widespread, and diverse group of early amniotes. To date only two fossils have been found in the rocks of South Africa. One of these fossils is an aggregation of five individuals.

<i>Tambachia</i> Extinct genus of amphibians

Tambachia is an extinct genus of dissorophoid temnospondyl within the family Trematopidae. It is known from the Early Permian Tambach Formation near the town of Tambach-Dietharz in Thuringia, Germany. Tambachia is the first trematopid to have been discovered outside the United States.

<span class="mw-page-title-main">Dissorophinae</span> Extinct subfamily of amphibians

Dissorophinae is a subfamily of dissorophid temnospondyls that includes Dissorophus and Broiliellus.

<span class="mw-page-title-main">Branchiosauridae</span> Extinct family of temnospondyls

Branchiosauridae is an extinct family of small amphibamiform temnospondyls with external gills and an overall juvenile appearance. The family has been characterized by hundreds of well-preserved specimens from the Permo-Carboniferous of Middle Europe. Specimens represent well defined ontogenetic stages and thus the taxon has been described to display paedomorphy (perennibranchiate). However, more recent work has revealed branchiosaurid taxa that display metamorphosing trajectories. The name Branchiosauridae refers to the retention of gills.

Scapanops is an extinct genus of dissorophid temnospondyl amphibian known from the Early Permian Nocona Formation of north-central Texas, United States. It contains only the type species Scapanops neglecta, which was named by Rainer R. Schoch and Hans-Dieter Sues in 2013. Scapanops differs from other dissorophids in having a very small skull table, which means that its eye sockets are unusually close to the back of the skull. The eye sockets are also very large and spaced far apart. Scapanops was probably small-bodied with a proportionally large head and short trunk and tail. Like other dissorophids, it probably spent most of its life on land.

<span class="mw-page-title-main">Eucacopinae</span> Extinct clade of amphibians

Eucacopinae is an extinct clade of dissorophid temnospondyls. Eucacopines differ from the other main group of dissorophids, the Dissorophinae, in having more lightly built skeletons and more knobby skulls. The subfamily was originally named Cacopinae, but since the name was already established for a group of living microhylid frogs in 1931, the name was changed to Eucacopinae in 2013. Eucacopinae is a stem-based taxon defined as the most inclusive clade containing the species Cacops apsidephorus but not Dissorophus multicinctus, which belongs to Dissorophinae. According to the most recent phylogenetic analyses of Dissorophidae, Eucacopinae includes the basal ("primitive") species Conjunctio multidens and Scapanops neglecta from the southwestern United States and a more derived ("advanced") group including several species of Cacops and the Russian genera Kamacops and Zygosaurus. Derived eucacopines have two rows of bony plates called osteoderms running down their backs, while the more basal eucacopines have only a single row. Dissorophines also have a double row of osteoderms but probably evolved them independently because the most recent common ancestor of the two groups had a single row of osteoderms.

Reiszerpeton is an extinct genus of dissorophid temnospondyl known from the Early Permian Archer City Formation of Texas. It is known solely from the holotype, MCZ 1911, a complete skull. This specimen was originally referred to the amphibamiform Tersomius texensis. A reappraisal of the holotype of T. texensis and a number of other referred specimens by Maddin et al. (2013) noted a number of differences from both T. texensis and amphibamiforms more broadly that suggested affinities with the Dissorophidae. This was confirmed by a phylogenetic analysis, which placed it as the sister taxon to the Eucacopinae. Reiszerpeton is known only from the type species, R. renascentis, which was named for Canadian paleontologist Robert Reisz. The species name refers to the recognition of Reisz as a "renaissance paleontologist." It is differentiated from other dissorophids by its small size, small and more numerous maxillary teeth, smooth cranial ornamentation, and greater distance between the orbit and the otic notch.

Barrosasuchus is a genus of peirosaurid notosuchian from the Santonian of Argentina and part of the extensive peirosaurid record of Late Cretaceous Patagonia. It contains one species, Barrosasuchus neuquenianus. B. neuquenianus is known from an almost complete skull and the majority of the articulated postcranial skeleton, making it the best preserved Patagonian peirosaurid.

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 13 DeMar 1968.
  2. ↑ Gee, B.M.; Bevitt, J.J.; Reisz, R.R. 2019. Dissorophid diversity at the early Permian cave system near Richards Spur, Oklahoma, USA. Palaeontologia Electronica 22(2):1-32. doi: 10.26879/976
  3. ↑ Cope. E.D. 1895. A batrachian armadillo. American Naturalist 29:998
  4. 1 2 DeMar 1966.
  5. 1 2 May et al. 2011.
  6. 1 2 Schoch 2012.
  7. 1 2 3 4 5 6 7 Williston 1910.
  8. ↑ Schoch & Sues 2013.
  9. ↑ Bolt 1974.
  10. 1 2 Carroll 1964.
  11. ↑ Dilkes 2009.

Sources

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